The present invention relates to the operation of solenoid valves for fuel in fuel injection systems, especially in the field of heavy-duty engines.
In injection systems for engines that are operated using a gaseous fuel, the fuel is generally metered using electromagnetically actuated gas valves. If the electromagnet is energized, a group of valve plates is moved counter to a return force exerted by one or more springs and opens up one or more flow-through openings. For closure purposes, the current is switched off. The group of valve plates is then pressed back onto the fixed valve seat, such that the valve is closed. This is what is known as a “normally closed” valve that is closed in the non-energized state, and in the process is ideally completely sealtight. Such valves are known for example from DE 10 2013 212 191 A1.
The lifetime of such a valve is typically a few hundred million load alternations. The main reason for the end of lifetime is a wear-induced undesired and uncontrolled increase in the injected amount of fuel, this being caused by two effects: the wear firstly reduces the residual air gap, such that the switch-off time increases. Secondly, the wear increases the stroke, such that the flow resistance of the valve is reduced. Another reason for the end of lifetime of a valve may be lack of sealtightness with respect to the intake manifold of the fuel injection system, which arises due to the wear in the region of the sealing faces between valve seat and valve plate.
DE 10 2014 220 795 A1 discloses a method for operating a solenoid valve injector in which wear-induced early closure is determined from the voltage signal of the electromagnet and is compensated by increasing the drive current for the electromagnet.